The theory behind and practice of RF heat ablation has been known for decades, and a wide range of suitable RF generators and electrodes exists. For example, equipment for causing heat lesions is available from Radionics, Inc., located in Burlington, Mass. A research paper by E. R. Cosman, et al., entitled “Theoretical Aspects of Radio Frequency Lesions in the Dorsal Root Entry Zone,” Neurosurgery, Vol. 15, No. 6, pp. 945-0950 (1984), describes various techniques associated with radio frequency lesions and is hereby incorporated by reference herein in its entirety. Also, research papers by S. N. Goldberg, et al., entitled “Tissue Ablation with Radio Frequency: Effect of Probe Size, Gauge, Duration, and Temperature on Lesion Volume,” Acad. Radiol., Vol. 2, pp. 399-404 (1995), and “Thermal Ablation Therapy for Focal Malignancy,” AJR, Vol. 174, pp. 323-331 (1999), described techniques and considerations relating to tissue ablation with radio frequency energy and are hereby incorporated by reference herein in its entirety.
Examples of high frequency generators and electrodes are given in the papers of entitled “Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone,” by Cosman, E. R., et al., Neurosurg 15:945-950, 1984; and “Methods of Making Nervous System Lesions,” by Cosman, E. R. and Cosman, B. J. in Wilkins R. H., Rengachary S. S. (eds): Neurosurgery, New York, McGraw-Hill, Vol. III, pp. 2490-2498, 1984, and are hereby incorporated by reference herein in their entirety.
The use of radiofrequency (RF) generators and electrodes in neural tissue for the treatment of pain and functional disorders is well known. Included herein by reference, an as an example, the RFG-3C Plus RF Generator of Radionics, Inc., Burlington, Mass., and its associated electrodes are used in the treatment of the nervous system, and the treatment pain and functional disorders. The RFG-3C Plus generator has one electrode output jack for connection to a single active electrode, and it has one reference electrode jack for connection to a reference electrode. When the active electrode is inserted into the body, and the reference electrode is placed, typically on the patient's skin, then RF current form the RF generate flows through the patient's body between the two electrodes. The generator can be activated and its signal output can be applied between the electrodes. Typically, this is referred to as a monopolar configuration because the active electrode is of smaller area than the reference electrode, and so the concentration of RF current is highest near it and the action of the RF electric field, whether for heating or for pulsed RF field therapy is greater there. This usually referred to as a single electrode configuration since there is only one “active” electrode. Parameters that can be measured by the RFG-3C Plus RF generator include impedance, HF voltage, HF current, HF power, and electrode tip temperature. Parameters that may be set by the user include time of energy delivery, desired electrode temperature, stimulation frequencies and durations, and level of stimulation output. In general, electrode temperature is a parameter that may be controlled by the regulation of high frequency output power. Existing RF generators have interfaces that allow the selection of one or more of these treatment parameters, as well as various methods to display the parameters mentioned
The use of high frequency electrodes for heat ablation treatment of functional disease and in the destruction of tumors is well known. One example is the destruction of cancerous tumors of the kidney using radio frequency (RF) heat ablation. A paper by D. W. Gervais, et al., entitled “Radio Frequency Ablation of Renal Cell Carcinoma: Early Clinical Experience,” Radiology, Vol. 217, No. 2, pp. 665-672 (2000), describes using a rigid tissue perforating and penetrating electrode that has a sharpened tip to self-penetrate the skin and tissue of the patient. This paper is hereby incorporated by reference herein in its entirety.
Four patents have issued on PRF by Sluijter M. E., Rittman W. J., and Cosman E. R. They are “Method and Apparatus for Altering Neural Tissue Function,” U.S. Pat. No. 5,983,141, issued Nov. 9, 1999; “Method and System for Neural Tissue Modification,” U.S. Pat. No. 6,161,048, issued Dec. 12, 2000; “Modulated High Frequency Tissue Modification,” U.S. Pat. No. 6,246,912 B1, issued Jun. 12, 2001; and “Method and Apparatus for Altering Neural Tissue Function,” U.S. Pat. No. 6,259,952 B1, issued Jul. 10, 2001. These four patents are hereby incorporated by reference herein in their entirety.
United States patents by E. R. Cosman and W. J. Rittman, III, entitled “Cool-Tip Electrode Thermal Surgery System,” U.S. Pat. No. 6,506,189 B1, date of patent Jan. 14, 2003, and “Cluster Ablation Electrode System,” U.S. Pat. No. 6,530,922 B1, date of patent Mar. 11, 2003, and “Cool-Tip Radiofrequency Thermosurgery Electrode System For Tumor Ablation”, U.S. Pat. No. 6,575,969 b1, date of patent Jun. 10, 2003, describe systems and methods related to tissue ablation with radiofrequency energy and electrodes and are hereby incorporated by reference herein in their entirety. One electrode system described in these patents comprises an electrode with an insulated shaft except for a fixed uninsulated tip exposure of an uninsulated exposed length, the electrode being internally cooled so that the uninsulated exposed tip is cooled. The electrode shaft is a rigid and self tissue piercing with a sharp pointed distal tip on the electrode shaft. This is essentially the configuration of cooled electrode offered by the Radionics Cool-Tip Electrode System (Radionics, Inc., Burlington Mass.) and the Valley Lab Cool-Tip Electrode System (Valley lab, Inc., Boulder Colo.) that are described later in this section. This design of electrode has one disadvantage that the initial insertion of the electrode can encounter tissue resistance which will displace the target volume, for example against a firm cancerous tumor, making it difficult to accurately position the electrode tip at the desired target tissue. It has another disadvantage that the clinician must inventory a multiplicity of electrodes having different lengths of tip exposure to accommodate his needs to create ablation volumes of different sizes, for example, to accommodate different sizes of tumors to be ablated. Another electrode system described in these patents comprises a system of a fully insulated cannula, a pointed stylet that can be inserted into the cannula so that the sharpened tip of the stylet just emerges from the distal tip end of the cannula when the stylet hub engages the cannula hub, and a separate cooled uninsulated electrode that can be inserted into the cannula when the stylet has been removed. The electrode length is greater than the stylet length so that the distal end of the electrode extends beyond the end of the cannula distal tip by a predetermined length when the hub of the electrode engages with the hub of the cannula, and the amount that it extends beyond the cannula tip is greater than the amount that the stylet extends beyond the cannula tip when the stylet is inserted into the cannula. One disadvantage of this electrode system design is that the stylet does not protrude to an equal degree beyond the cannula tip as the electrode, so that the pointed stylet does not produce a tract in the target tissue that can facilitate insertion of the electrode tip to the desired target. Another disadvantage is that the sharp stylet does not extend significantly from the distal end of the cannula, so that the cool electrode when inserted into the cannula, after the stylet has been removed, must push through and penetrate the bodily tissue until the distal tip of the cool electrode reaches a desire to target position within the tissue, for example, at an appropriate point inside a tumor that is to be ablated.
The Cosman G4 Radiofrequency generator (Cosman Medical, Inc., Burlington, Mass.) is another example of a modern RF lesion generator and the brochure printed in 2011 is hereby incorporated by reference herein in its entirety.
The Radionics Cool-Tip Electrode System (Radionics, Inc., Burlington Mass.) and the Valley Lab Cool-Tip Electrode System (Valley lab, Inc., Boulder Colo.) are existing examples of cooled radiofrequency electrodes designed to ablate tissue in the living body, an example of which is ablation of tumors. The brochures for these products are hereby incorporated by reference herein in its entirety. These electrodes systems comprise an electrode that has a partially insulated shaft, an uninsulated distal tip of known uninsulated length, and the distal tip is sharpened so that the electrode can pierce tissue and the bodily tissue to be positioned in a target position in the living body. The uninsulated tip, and the electrodes connected to the output signal of a high frequency generator, will produce heating of the bodily tissue near the tip. The electrodes are also cooled by an internal fluid cooling system, and this has the effect of producing larger ablation volumes which can be desired, for example, to coagulate large tumors. One disadvantage of these electrodes is that they are supplied sterile packaged and have a fixed uninsulated tip of a known length. This means that the manufacture and the hospital user must inventory a range of these electrodes with various lengths and tip exposures to accommodate a tumor size related to a specific patient. Another disadvantage space is that the sharpened distal end is in the shape of a trocar point, and this produces a significant resistance force when inserting the tissue piercing electrode into the bodily tissue. This can cause displacement of the tissue, especially full firm tissue and for firm tumor target volumes. An additional disadvantage of the trocar point of this prior art is that it is a solid metal piece several millimeters in length into which coolant does not flow, thereby limiting cooling of tissue in contact with the distal point of the electrode where the rate of tissue heating can be highest, and limiting prevention of tissue boiling which can limit heat lesion size. Another disadvantage of the trocar point on the active tip of this prior art is that it includes points of high curvature which can induce high focal electric fields, tissue heating, boiling, the production and migration of gas bubbles, elevated impedance, and thus limit heat lesion size. A further disadvantage of these electrodes is that they have large hubs which are greater than 15 mm in diameter and are several inches in length. These large hubs are necessary according to the design so that the clinician can have sufficient manual grip on the hub to implement the forceful self piercing and penetration manipulation of the electrode through the patient's skin and fur the wrong into the target volume within the bodily tissue, as for example, into a cancerous tumor that is deep within the body. This disadvantage means that the electrode systems are bulky and present a heavy and large hub structure. this can have the disadvantaging of producing undesired torque and forces on the electrode when inserted into the body causing potential inaccuracy and shift of positioning the electrode distal tip with respect to a desired target position in the tissue. The large and bulky hubs have another disadvantage that is more difficult to insert multiple independent electrodes into the body in a tight cluster, because the large hub diameter limits the closeness with which the electrodes and the hubs can be clustered. In one case, this can be disadvantageous when multiple electrodes are being passed between the space between the ribs to access, For example, a cancerous tumor in the liver or in the lung.
In a patent by Mark Leung, et al., entitled Electrosurgical Tissue Treatment Method, U.S. Pat. No. 7,294,127 B2, date of patent: Nov. 13, 2007; and, in another patent by Mark Leung, et al., entitled Electrosurgical Tissue Treatment Method, U.S. patent number 2005/0177210 A1, date of patent: Aug. 11, 2005, a cooled RF electrode is shown for an application in the field of pain therapy for bipolar lesion making in the spine. These patents are hereby incorporated by reference herein in its entirety. The Baylis Medical Company offers a commercial version of the design shown in the patent these two patents, and the brochures for these products are hereby incorporated by reference herein in its entirety. These two patents and the Baylis product describes a system of an insulated cannula with introducing stylet that emerges by a few millimeters from the distal end of the cannula, and substantially less than 10 mm. A high-frequency electrode can be inserted into the cannula, when the introducing stylet has been removed, and the electrode has a distal end which emerges from the end of the cannula when the hub of the electrode in the cannula hub are engaged together. The distal end of the electrode will emerge from the distal end of the cannula by a different distance than the distance that the distal end of the stylet from the cannula when the stylet is inserted into the cannula. In one electrode system of the Baylis products, the TransDiscal electrode, the high-frequency electrode also is adapted so that its distal portion that emerges beyond the distal end of the cannula has a partially insulated portion, and has an uninsulated exposed distal tip of the electrode that is approximately 6 mm in length. In the Baylis products referred to by Baylis as Sinergy, Transdiscal, and Thoracool, the length of the uninsulated exposed conductive tip portion that is used to energize the tissue around the tip is between 4 and 6 mm. When the electrode is connected to the output signal of a high-frequency generator, it is the uninsulated exposed distal tip of the electrode which is used to create the thermal ablation. In all Baylis products, the high-frequency electrode shaft is completely insulated over the entirety or almost the entirety of the portion of the shaft that is inside the cannula, when the electrode hub is fully engaged with the cannula hub. One disadvantage of this design is that it either does not, or does not reliably, enable high frequency output signal to be conducted between the electrode and the cannula. The cannula that is being used is insulated over its entire length, including right up to the distal tip end, so that the cannula does not have any uninsulated portion to energize tissue that surrounds the cannula when the cannula is inserted into bodily tissue. As a consequence, when the electrode is connected to the output signal of a high-frequency generator, the cannula itself does not deliver any output signal to the tissue in which it is placed. The high-frequency electrode is also cooled by an internal fluid channel's that carry cooled fluid from a fluid supply external to the electrode that can be connected to the electrode by tubes. The electrode of these designs has a hub which has a diameter of greater than 13 mm. One disadvantage of TransDiscal Baylis electrode design is that the portion of the electrode that emerges from the cannula is not completely uninsulated. Another disadvantage of this design is that the cannula is completely insulated preventing thermal ablation over the portion of the cannula shaft distal tip. Another disadvantage of this design is that the high-frequency electrode does not make reliable electrical contact with the cannula when the electrode is connected to a high-frequency generator. The design of the fluid channel's in the electrode hub of the devices shown the two referenced patents and in the Baylis brochures comprise input and output fluid tubes into the hub structure in the input and output fluid tubes are connected to fluid carrying tubes that extend inside the electrode shaft and down to the distal end of the electrode shaft. This design has the disadvantage that the input and the output tubes are incorporated within the hub structure, and the inflow and the outflow internal tubes within the electrode shaft occupying a lateral displacement equal to the sum of the diameters of the internal tubes. These factors have the disadvantages that the hub diameter of the Baylis cooled RF electrode is 13 mm. This has the disadvantage that the diameter is sufficiently large that it restricts the use of multiple such Baylis electrodes in a cluster where the electrodes are inserted into the tissue in a parallel array with the distance between the hubs less than 13 mm. Another disadvantage is that the cooling efficiency at the tip of the high-frequency electrode is reduced by the fluid impedance of the two internal tubes that extend inside and along the entire length of the electrode shaft. Another disadvantage is that the Baylis electrode designs is that they have an exposed electrode tip length of only approximately 4 to 6 mm, and this is insufficient for ablation of large target volumes such as large cancerous tumors which can be, in a in typical cases greater than 1 cm in dimension, and in other typical cases up to 4 cm, or 5 cm, or more in dimension. In all of the Baylis products, the electrode shaft comprises a plastic tube with delicate flexible cooling tubes within. Only over approximately up to 6 mm of the distal tip end if the shaft's outer material a conductive metal. This has one disadvantage that the shaft is not robust to high longitudinal or pushing force is as the electrode is passed into bodily tissue. Another disadvantage of the plastic shaft is that it is not robust to lateral bending forces.
A wide variety of radiofrequency electric configurations are offered by Cosman Medical, Inc. One example is the TIC Kit which comprises for equal length cannulas, each having different and known uninsulated distal tip lengths. The Kit also comprises a stylet which can be inserted into each cannula to produce a sharpened occluded tip for the combination of the cannula with the stylet when the stylet is inserted into the cannula so that the hub of the cannula and the hub of the stylet are engaged with each other. The Kit also includes a fully uninsulated high frequency electrode that can be inserted into each of the cannula, when the stylet has been removed, so that when the electrode is connected to the output signal of a high-frequency generator, then the output signal will energize the uninsulated distal tip of the cannula. The electrode has an indwelling temperature sensor in its distal tip so that when the electrode is inserted into the cannula with the hub of the electrode is engaged with the hub of the cannula, the temperature sensor will measure the heating temperature corresponding to heating of the tissue around the uninsulated tip of the cannula. This electrode system was designed for coagulation of the trigeminal nerve to treat trigeminal neuralgia. One disadvantage of this design is that electrode system is not adapted to be cooled by an internal cooling fluid, so this system is not suitable for ablation of large target volumes such as for cancerous tumors. Another disadvantage of this design is the uninsulated exposed distal tip lengths of the cannula are not greater than 10 mm, which is not adequate for most ablations of cancerous tumors.
The present invention overcomes the stated disadvantages and other limitations of the prior art.